Irrigation control systems known in the art typically employ a time clock and controller coupled to one or more electrically actuated or activated valves. These systems typically use predetermined watering time periods which are set by programming of the irrigation controller. The programming of such controllers may include dial settings, digital control settings, placement of mechanical pegs or stops, or some other manipulation of the time clock or controller settings.
When a predetermined watering start time occurs, one or more of the associated irrigation valves are opened. The irrigation valves are open for a pre-programmed watering period and then closed under the control of the time clock after such watering period has run.
Considerable inefficiency and poor performance can result when using pre-programmed watering controls as described above. For example, such watering systems typically irrigate during rain storms, thus resulting in wasted water. They also irrigate without consideration of the temperature of the air or ground, and without considering the ground moisture actually present.
Another area of concern involves multi-zone systems which may have one or more of the zones which are insufficiently watered, resulting in dry areas while other zones have sufficient or excess water. This results in particular zones within a multi-zone system which are inadequately watered, while other zones are watered to excess, thus producing dry areas, waterlogged areas, water wastage and derogatory effects on the grass or other crop being irrigated.
Conventional systems using predetermined watering time periods are adjusted to try and account for zonal variations by only using watering time as an adjustable parameter. However, the differences which are satisfactory during one season or weather period may not be satisfactory during a different season or weather period. Also, daily temperature and other daily or episodal weather fluctuations may not be adequately compensated for using watering time periods set under prior conditions and previously observed results.
Attempting to eliminate such problems under a pre-programmed, time-based watering scheme requires tedious, trial and error adjustments to the irrigation controller. These adjustments typically deliver results which are an attempt to provide proper control for the circumstances just experienced, but are not satisfactory under current changes and variable future conditions. For example, one set of adjustments made during mild weather may yield undesirable results during hotter, dryer weather conditions which may begin the day after an adjustment has been made. Thus, it is impossible to provide optimal watering using such systems and in most cases it is difficult to provide even good watering schedules in light of constantly changing seasonal, episodal and daily weather patterns and fluctuations.
Another approach is to use ground moisture sensors. Although this seems like a reasonable approach, it has been found extremely difficult to achieve with good results. Some moisture sensors have been attempted based upon detecting the electrical conductance of surrounding soil. The conductance of soil is variable dependent upon moisture content. However, variations in soil conductivity are dependent not only on moisture content but also upon the composition of the soil. The variety of different soil types and soil constituents that affect conductivity are numerous and are difficult to predict or account for in a reliable manner. Thus a system adapted for one area may not work in another.
Of particular significance are the amounts and types of salts available in a given type of soil. These vary to a great extent from one location to another. Other important causes of variations in soil conductivity are associated with variations in soil acidity or alkalinity (soil pH variations). These also have significant effects on the conductivity of the soil and make it difficult to reliably determine moisture for various soils. Accordingly, such variations make determining ground moisture using conductive sensors unreliable.
In addition to variations from soil types, pH levels and location to location, there are also significant variations over time for a given location. Further significant are common changes which may occur due to application of chemicals, such as application of fertilizers, lime, and other treatment chemicals frequently applied to lawns, crops, and other irrigated areas. These chemicals can dramatically affect the conductivity of the soil and thus prevent meaningful moisture measurements from being made using conductive and other prior types of sensors. Thus, it has been difficult or impossible to reliably measure soil moisture using prior conductive and other sensing systems.
The problems indicated above also suggest similar problems with capacitive moisture sensors and irrigation systems based thereon. As the inventors have now discovered, the above problems have been furthered by extraneous ground currents that run through the soil from electrically operated sprinkler zone control valves, electrical and telephone grounding rods, and other miscellaneous sources of electrical current that inject or induce currents into the ground. Capacitive sensors have been particularly susceptible to producing unreliable results, in part because of such stray currents.
Thus, there remains a need for an irrigation control system and related methods and apparatuses which provide improved watering control based on the actual watering needs of the irrigated zone or zones, while reducing or eliminating wasted water and preventing frequent manual adjustment of the controller due to daily, episodal or seasonal fluctuations in weather conditions. Such a system is needed which preferably provides reliable operation based on moisture content despite application of fertilizers, pesticides, herbicides and other chemical treatments which may be routinely applied to the soil being irrigated.